FIELD OF THE INVENTION
The present invention relates to a dielectric resonating device and particularly to a dielectric resonating device having therein a plurality of transverse magnetic (TM) dielectric resonators which together constitute a bandpass filter.
In a dielectric resonating device, an oscillation mode of a dielectric resonator fixed in a shield case and sectioned by a metallic plate is known to be the TM.sub.010 mode as indicated for example in Japanese Patent Publication No. 50401/1986.
In a conventional dielectric resonating device, a dielectric resonator body 2 is positioned in a cylindrical case 1 as shown in FIG. 1. A plate 3 of a disc shape is fixed on the inner wall of the cylindrical case 1, forming two resonators. The dielectric resonator body 2 penetrates a hole formed in the plate 3 and a gap 4 is defined between the dielectric resonator body 2 and the plate 3 for coupling between the two resonators.
In the above described structure of the conventional device, a high dimensional precision is required in the gap 4 for adjustment of a coupling coefficient because the coupling gap 4 is formed in a region exposed to a high field strength, close to the dielectric resonator body 2. Accordingly, it is difficult to obtain a desired coupling coefficient. In addition, in order to maintain a stable state in the gap 4 with respect to temperature change, the cylindrical case 1 and the plate 3 need to be formed by a material having the same coefficient of linear expansion as that of the dielectric resonator body 1. If a stable coupling coefficient is to be obtained for that reason, the range of materials that can be used considerably limited.
In the device of FIG. 1, input/output connectors 5 are fixed to both ends of the cylindrical case 1. Internal conductors 6 of the connectors 5 are fitted fixedly in holes 8 formed in both ends of the dielectric resonator body 2 through holes 7 of the cylindrical case 1, whereby the connectors 5 and the dielectric resonator body 2 are connected.
Since the internal conductors 6 are hidden in the respective holes 8 in the above described structure, it becomes difficult to adjust a coupling condition between an external circuit and the resonator once the internal conductors are fitted fixedly in the holes 8.